Optical memory technology that uses optical disks having a pit pattern as high-density, large-capacity information storage media has been used in an increasingly expanded range of applications from digital audio disks to video disks, document file disks, and further to data files, etc. In recent years, a high-density optical disk such as a DVD-ROM using a visible red laser of wavelength of 630 nm to 670 nm as a light source has become prevalent. Furthermore, an optical disk (DVD-RAM) capable of high-density recording has been commercialized. A large capacity of digital data has been able to be recorded on an optical disk easily. Furthermore, CD-R that is highly compatible with CD technology, which has been used broadly, has been prevalent. CDs (CD, CD-R, CD-RW) have a base material thickness of about 1.2 mm, and DVDs (DVD-ROM, DVD-RAM, or the like) have a base material thickness of about 0.6 mm. Throughout this document, the term optical disk is used generically to refer to optical storage disks such as DVDs and CDs.
Portable optical disk players (like DVD players and CD players) are becoming increasingly popular. Two of the important differentiating factors of these portable players are (1) small size and (2) lower power consumption. Small size contributes to lightweight portable devices that consumers want. Low power consumption allows for longer battery lifetimes of the devices. These longer battery lifetimes increase consumer satisfaction. A need exists for a way to make optical disk players that are smaller and use less power.
Current methods for reading optical disks include directing a laser upon the pits or bumps within the tracks of the optical disk. The majority of this beam (the “processing portion”) is reflected off the optical disk and is incident upon photodetectors that then convert the photonic signal into an electric signal representing the bits stored on the optical disk. As the optical disk spins, it may wobble (especially in a portable player) and the processing portion of the beam may either go out of focus or off the track on the disk. A need exists for a way to ensure that the processing portion stays focused in the center of the track to ensure accurate reading of the disk.
In U.S. Patent Application No. 20030007436, entitled, “Optical pick-up, optical disk apparatus and information processing apparatus,” this beam tracking is handled by diffracting a tracking portion of the laser with a binary grating, such that it is incident on the “land” of the optical disk between tracks. This tracking portion of the beam is reflected at a different angle and is measured with a separate photodetector than the processing portion. A problem remains that a third portion of the beam is lost due to inefficiencies in the binary grating. In one example, 75% of the beam is used for reading the disk, 9% of the beam is used for tracking, and 16% of beam energy is lost due to unused diffraction orders. If the lost energy could be utilized for either reading or tracking, a less powerful laser could be used within optical disk devices (like DVD/CD readers and writers), which would lower the costs of producing and operating these devices. Therefore, a need exists for a way to decrease the inefficiencies in diffracting a portion of the laser beam used in optical disk devices.
It is an object of this invention to make optical disk drives that are smaller and use less power.
It is another object of this invention to ensure that the processing portion stays focused in the center of the track to ensure accurate reading of the disk.
It is yet another object of the present invention to increase the efficiency of the optical path of the laser beams used in optical disk devices.
It is yet another object of the present invention to decrease the inefficiencies in diffracting a portion of the laser beam used in optical disk devices.